The Huygens-Fresnel diffraction integral has been formulated for incident spherical waves. A source of a spherical wave is kind of intuitive, since the perpendicular rays of the sphere converge into a single point, which we can call the punctual source.

On the other hand, if we approximate the Huygens-Fresnel principle into parabolic -or paraboloidal- wavefronts (Fresnel diffraction), how can we understand the source of such wavefront, by the fact that the normal lines of the paraboloid does not converge into a single point?

  • $\begingroup$ Why do you need to know ? I mean, do you think you need it for further calculations, or you are just curious whether and how it is possible ? (BTW it could result of parallel or spherical wavefronts after reflection or refraction on a dedicated shape). $\endgroup$ – Fabrice NEYRET Oct 30 '15 at 17:29
  • $\begingroup$ because parabolic waves look like they are more realistic, since punctual sources do not exist, I expect the parabolic wavefront are produced not by a punctual source but a spot with some dimension, namely the Fresnel diffraction would be an approximation to non punctual sources. $\endgroup$ – E.phy Nov 3 '15 at 15:50
  • $\begingroup$ well, the very notion of unique front (= all in phase) might be ill-posed, then. $\endgroup$ – Fabrice NEYRET Nov 3 '15 at 15:55
  • $\begingroup$ I suspect the parabolic front is just the first added complexity to linear front in the spirit of Taylor series. (but maybe I'm wrong). $\endgroup$ – Fabrice NEYRET Nov 3 '15 at 15:57

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